Soft iron

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Pieces of soft iron from the core of a transformer

Soft iron is a soft magnetic material for magnetic cores and consists of unalloyed iron with a high degree of purity. The word "magnetic iron" is occasionally used as a synonym, even if this term actually refers to the oxidic iron mineral magnetite . Soft iron is produced either from powder using a sintering process or using a melting process in a vacuum.

In the past, electrical machines in particular ( electric motor , generator and transformer ) contained soft iron sheets to bundle the required magnetic fields . Today, dynamo sheet metal (iron-based alloys) is mostly used for this , which has a lower electrical conductivity due to an additional alloy of around 3% silicon and thus reduces eddy current losses in AC operation.

Soft magnetic materials are always used when temporary magnetization by an external magnetic field should not lead to permanent magnetization. This is also the case with moving-iron measuring mechanisms , for example . A basic requirement for this is a low coercive field strength , which is a quality feature for soft iron alloys. Powder-sintered soft irons tend to have a lower coercive field strength than those produced using vacuum melting processes, but they are significantly more expensive.

Nowadays, soft iron plays an important role in magnetic shields and in magnetic flux guidance (constant field yokes, magnetic pole pieces , relay parts ). In contrast to the more highly permeable nickel-iron alloy mu-metal , soft iron is mainly used in the area of strong magnetic fields. Due to the high saturation magnetization of approx. 2.15 Tesla compared to mu-metal , soft iron enables a higher field strength density with a comparable material thickness of the shield or the yoke. That is why it is sometimes used for shielding and flux modeling of permanent magnets . Soft iron is also used in some cases to cover clockworks in wristwatches.

literature

Richard Boll: Soft Magnetic Materials - Introduction to Magnetism . 4th edition. Hanau 1990, ISBN 3-8009-1546-4 , p. 177; 278-279 .

Web links

Commons : Soft Iron - Collection of images, videos and audio files

Individual evidence

^ H. Danan, A. Herr, AJP Meyer: New Determinations of the Saturation Magnetization of Nickel and Iron . In: Journal of Applied Physics . tape 39 , no. 2 , February 1, 1968, ISSN 0021-8979 , p. 669-670 , doi : 10.1063 / 1.2163571 ( scitation.org [accessed December 9, 2017]).

[1] H. Danan, A. Herr, AJP Meyer: New Determinations of the Saturation Magnetization of Nickel and Iron . In: Journal of Applied Physics . tape 39 , no. 2 , February 1, 1968, ISSN 0021-8979 , p. 669-670 , doi : 10.1063 / 1.2163571 ( scitation.org [accessed December 9, 2017]).